fix(input): allow use of integers in ng-true-value

Request Type: bug

How to reproduce: PR for: https://github.com/angular/angular.js/issues/7109

Plunker from that issue: http://plnkr.co/edit/VxJVpbRV4vkbivKpAUUn?p=preview

Component(s): forms

Impact: medium

Complexity: small

This issue is related to: 

**Detailed Description:**



**Other Comments:**

Resolves an issue where values of '1' in ng-true-value would not set the
checkbox to a checked state when the scope's value was 1.

Closes #7109